This invention relates generally to the creation of process color (i.e. spot on spot) images in a single pass and more particularly to the use of light lens image scanning techniques for such purposes.
In the document reproduction art, an original document to be reproduced is typically placed on a stationary platen and illuminated by a incremental line-scanning optical system. Reflected light rays from the document travel along an optical path and are projected by a lens on to a photosensitive imaging member thereby forming latent electrostatic image thereon. The latent image of the document formed on the imaging member is then developed by appropriate marking material such as toner, and then the developed image is transferred to a record medium such as plain paper. Various types of scanning mechanisms are known in the art, but the most widely used utilizes a pair of guide rails which are mounted in a parallel plane beneath the document platen. The scanning components are mounted on one or more movable scan carriages which are driven by a cable arrangement to run back and forth beneath the platen and supported by the guide rails. Examples of such prior art scanning systems employing an elongated illuminated lamp and scan mirrors to scan/illuminate the document are shown in U.S. Pat. Nos. 4,367,945, 4,155,641 and 4,603,963.
Alternatively, the document to be reproduced has been scanned by a Raster Input Scanner (RIS), typically a CCD sensor array. The RIS type scanner is supported for movement beneath the document platen and is moved in the scan, re-scan direction by a scan assembly basically similar to the ones used in the above-identified patents relating to light lens imaging.
Following is a discussion of additional prior art, incorporated herein by reference, which may bear on the patentability of the present invention. In addition to possibly having some relevance to the patentability thereof, these references, together with the detailed description to follow, may provide a better understanding and appreciation of the present invention.
U.S. Pat. No. 4,937,636 granted to Rees et al describes one technique that involves tri-level imaging in a light lens copier for creating highlight color images in a single pass. In that patent, an original to be copied is modified using fluorescent ink on selected portions thereof. Light reflected from the modified original is transmitted through a colored filter and is projected onto the surface of a monopolar photoreceptor. Light incident on the fluorescent ink is absorbed over a specific wavelength range and is re-admitted at a higher wavelength. This light, and light reflected from the white background, are transmitted through a filter of a color associated with the re-emited wavelength. Light reaching the photoreceptor discharges charged areas thereon at two energy levels. The resulting latent image incorporates three separate discharge levels corresponding to the black image information, color fluorescent areas, and background areas. The black and color areas are developed with appropriate colored toner by developer units biased at the appropriate levels. The requirement modifying an original using special inks presents a serious drawback to commercial acceptance of the process.
U.S. Pat. No. 3,832,170 Nagamatsu et al., describes a photosensitive member having an insulating layer acting as a color filter. The photoconductive drum is divided into three segments, each segment corresponding to a different colored electrostatic latent image. These differently colored electrostatic latent images are then developed by toner particles complementary in color thereto. The toner powder images are then transferred to a copy sheet in superimposed registration to form a multicolor copy corresponding to the original document.
U.S. Pat. No. 4,078,929 Gundlach, discloses a reproduction machine which can form a two color copy of an original document either using conventional light lens exposure techniques, or electronically. A charge pattern of a single polarity and having at least three different levels of potential is formed on a photoreceptor and developed in two colors by utilizing relatively negatively charged toner particles of one color and relatively positively charged toner particles of a second color. The exposure system requires the use of black and white images on an original document having a intermediate (grey) color.
U.S. Pat. No. 4,189,224 Sakai, discloses a photoconductive drum formed with first and second photoconductive layers of different spectral sensitivities. The photoconductive drum is charged and exposed causing electrostatic latent images to be formed on the respective layers according to the color within the original document. The charges of the latent images are of opposite polarity. Toner particles, similarly of opposite polarity, are used to develop the respective latent images. The toner particles of different colors. In this way, a two-color copy is formed.
U.S. Pat. No. 4,264,185 Ohta, describes an electrophotographic printing machine employing a photoconductive drum formed with at least two photoconductive layers of different spectral sensitivities. One layer may be panchromatic with the other layer being insensitive to red light. The drum is charged, at least twice, with opposite polarities to produce the charge pattern. A light image of the original document then exposes the charged regions of the drum. This results in positive and negative electrostatic latent images being recorded thereon. The latent images are developed with black and red toner particles of opposite polarity to form a two-color copy.
U.S. Pat. No. 4,335,194, Sakai, discloses a photoconductive member comprising a red sensitive photoconductive layer and a redinsensitive photoconductive layer. Two colors are printed by charging and exposing to white light, irradiating with red light and charging to an opposite polarity, charging to the same polarity as an opposite polarity, charging to the same polarity as the first polarity, and developing with red and black toners of opposite polarity.
U.S. Pat. No. 4,509,850, Weigl, teaches an electrophotographic printing machine capable of reproducing both black information and red information in a single pass. A continuously charged area and a modulated charged area are recorded onto a photoconductive surface. The modulated charged area is developed with polar or polarizable marking particles of a first color while the continuously charged area is developed with charged marking particles of a second color.
U.S. Pat. No. 4,479,242, Kurata, discloses a dichromatic reading device capable of separating a specific color from other colors of and original document. An electric circuit is provided which obtains the difference between the level of an image signal readout without a filter, and the level of a signal readout through a complementary filter for the specific color. Subsequently, an image signal for the specific color is produced from the difference.
U.S. Pat. No. 4,068,938, Robertson, teaches an electrophotographic printing machine capable of reproducing two color copies from a two color original document. An electrostatic latent image having three discrete potential levels is recorded onto a photoconductive drum. A high level is developed by particles of a first color corresponding to a dark color of the original document and a low level is developed by particles of a second color. The underdeveloped portion remains the color of the sheet of support material.
U.S. Pat. No. 4,562,129, Tanaka, discloses a bipolar photoreceptor which permits three different potential levels to be formed thereon.
U.S. patent application Ser. No. 08/301,922 discloses a twopass, light/lens, highlight color copier in which large contrast images are created providing relatively large development fields or potentials compared to those associated with tri-level imaging.
U.S. patent application Ser. No. 08/237,945 filed on May 2, 1994 discloses a method and apparatus for forming orthographic color images. A relatively high resolution ROS is utilized to simultaneously form a plurality full contrast images thereby yielding the registration precision available in tri-level imaging while providing full contrast images of conventional xerography as discussed above.
U.S. Pat. No. 5,493,387 granted to VonHoene et al on Feb. 20, 1996 discloses apparatus for creating highlight color images in a single pass using a light lens copier. Image exposure is accomplished using light/lens scanning of a multi-color original together with simultaneous shunting. Using a special overcoated photoreceptor configuration and a sequence of image creation steps including the aforementioned simultaneously shunting and exposure step, balanced latent images are formed across the photoreceptor structure. By balanced is meant that latent images exist across both an overcoat layer of the photoreceptor and the rest of the photoreceptor. Such an arrangement precludes development of the image across the overcoat layer if the photoreceptor were to be moved past a development system. Thus, an electrostatic voltmeter used to read the surface potential in the image areas would read zero or near zero volts. Following formation of the a plurality of balanced images, each of the balanced images is, one at a time, caused to become unbalanced prior to its movement past an appropriate development system. Such unbalancing is effected using a low resolution ROS or other suitable exposure device. Each low resolution ROS would provide full exposure sufficient to discharge the photoreceptor leaving the portion.
U.S. patent application Ser. No. 08/368,130 filed on Jan. 3, 1995 discloses apparatus for creating highlight color, gray scale imaging using light lens scanning of an original document. A Raster Input Scanner (RIS) which scans the original document is utilized for controlling the illumination intensity of one or more low resolution exposure devices. Information gathered by the RIS also controls the particular image area to be developed.
U.S. patent application Ser. No. 08/368,140 filed on Jan. 3, 1995 discloses highlight color imaging apparatus wherein the images which are formed in a single pass image are charge neutralized prior to subsequent exposure and development steps. A Photoreceptor image receiver is selectively discharged using low resolution exposure devices.